This invention relates to a process for producing substantially homogeneous mixtures of reactive substances.
In chemical engineering there are numerous processes for mixing together substances reactive with one another in such a way that they react with one another in a desired way. The great number of processes reflect the problem of producing mixtures. It is thus common to work in diluting solvents which simultaneously serve to supply or remove energy, whereby all reacting components present are dissolved in the solvent or the reacting agents are united gradually, e.g. drop by drop. Other mixing techniques involve bringing together two educt streams in a reaction chamber, gradually dissolving or reacting a first component in a reacting medium containing one or more further components or controlling reactions by adding catalysts. It is common to use mechanical or other stirring tools to achieve a thorough mixture of the reacting medium necessary for the reaction. Nevertheless it is still problematic to produce a highly homogeneous mixture of reactive substances which is optimal for the particular purpose, in particular because the chemical reactions already start during the mixing process, i.e. before an optimal mixture of the components has taken place. This frequently detracts from the yield and purity of the products and results in increased costs for the products because of low yield, and the need for elaborate cleaning methods or complicated apparatus for producing the mixtures.
One also commonly tries to optimize chemical reactions by working in large quantities of solvent to influence the mixing behavior of the reacting agents and thus the reaction course via the diluting effect. Large quantities of solvent require elaborate recovery processes, apart from the fact that the quantities of solvent must not only be supplied but also handled, separated, cleaned/reprocessed or eliminated.
In particular in the conversion of highly reactive substances there can be undesirable consecutive reactions if one does not succeed in distributing the reacting agents homogeneously. Such distribution is problematic, however, when one substance must be mixed into a second one, as is frequently done in the laboratory with the help of dropping funnels. At the place where the added substance passes into the reacting medium a high concentration forms temporarily which, in the case of fast reactions, cannot be reduced using conventional mixers and stirrers fast enough to avoid merely pointwise conversion with consecutive reactions.
The same holds for the production and further processing of plastics when several reacting agents are present. Pointwise reaction can lead to changed reaction conditions at certain points and thus influence the nature, structure or distribution of the products. This also holds for example for catalyzed reactions when the catalyst is not distributed homogeneously. Such inhomogeneities also occur for example in the hardening of polyurethane foams when for example moisture-hardening foams full-harden with the entrance of atmospheric humidity from the outside to the inside, the second component in 2C foams is mixed incompletely with the first component and therefore reacts only locally, or reactions take place with introduced water, on the one hand, and with an added agent, on the other, in the recycling of prepolymer residues. Since the reactions take place in accordance with the availability of the reactive substances, inhomogeneities both impair the products and cause problems in carrying out recycling processes, in particular because the simultaneous presence of cans which are empty except for a small remainder, partly full cans or full but useless cans can cause different qualities of prepolymers, different quantities of hardeners and, in the case of cans that have become moist, also different quantities of water to be brought into the process. This results furthermore in a batch-dependent quality of the products.